1. Field of the Invention
The present invention relates generally to current sensors, and more particularly, to a current sensor which can be adjusted during manufacture to achieve a specific relationship between an electric current flowing through an opening of the current sensor and an output signal from the current sensor.
2. Description of the Prior Art
There are many devices known to those skilled in the art which can be used to measure the magnitude of an electric current. One particular device, commonly referred to as a current sensor, comprises a magnetically sensitive transducer associated with a magnetic flux concentrator. The current sensor has an opening that is shaped to permit an electrical conductor to be extended therethrough. When an electric current passes through the opening in the current sensor, it creates a magnetic field which is concentrated along a generally annular path by a magnetic flux concentrator. The flux concentrator is shaped to have a space formed in its circumferential length. The magnetically sensitive device, such as a Hall effect device, is disposed within the space. An output signal of the current sensor varies as a function of the flux density within the space which, in turn, varies as a function of the electric current flowing through the opening of the current sensor.
Although many different styles of current sensors are known to those skilled in the art, a typical current sensor comprises a magnetic flux concentrator which is made of a ferrite material. Some current sensors incorporate a linear output Hall effect transducer which is disposed within the space formed in the concentrator. In a device of this type, the output signal of the linear output Hall effect transducer provides a linear output voltage signal that tracks the waveform of the sensed current flowing through the opening of the current sensor. The output signal from the Hall effect transducer varies as a function of the current magnitude for either AC or DC currents. Current sensors of this type ar available in commercial quantities from MICRO SWITCH, A Division of Honeywell Inc. and are identified under numerous catalog listings in the CS Series.
As numerous different household appliances are provided with enhanced capabilities, the need for current sensors has significantly expanded. However, the widespread use of current sensors in appliances is restricted by cost considerations. Normally, inexpensive current sensors do not provide an output signal voltage that varies with a sufficiently consistent relationship to the measured current consistently from one current sensor to the next. Applications of current sensors in appliances require the ability to replace one inexpensive current sensor with another without having to recalibrate the current sensor to suit the appliance into which it is being installed. Current sensors which exhibit a consistent output voltage signal to measured current ratio which does not vary significantly from one current sensor to the next are typically too expensive for widespread use in appliances.
It would therefore be significantly beneficial if a low cost current sensor could be provided which was adjustable during manufacture to achieve a relatively precise relationship between its output voltage and the measured current so that the low cost current sensor could be replaced by another low cost current sensor without having to recalibrate the sensor for the particular application into which it is being installed. In order for appliances to be cost effective, all of the parts installed in the appliance must be interchangeable with other like parts made for the same purpose. The purpose of the present invention it to achieve an inexpensive current sensor which can be manufactured in such a way that each current sensor is interchangeable with any other current sensor of the sam type. This requires the ability to manufacture the current sensor in such a way that the relationship between the output voltage signal and the measured current is predictable an precise within a predetermined range of operation.